1. Field of the Invention
The present invention relates to a fuel injection quantity control device with specific operation when fuel injection in a diesel engine is restarted from a cut-off state.
2. Description of the Related Art
It is considered that the case in which an accelerator pedal is pressed and fuel injection is restarted from a state in which fuel injection in a diesel engine has been cut off for the prescribed time, for example, a state in which the accelerator pedal was released on a slope and engine brake was actuated. In this case fuel is injected into cylinders that were cooled because fuel injection was cut off for the prescribed time during which the vehicle was on the slope. As a result, if the fuel injection quantity is small, the entire injected fuel is not combusted properly and the non-combusted components are discharged as white smoke.
The following countermeasures are known for preventing the white smoke, causing a glow plug provided in a cylinder head to generate heat during the fuel injection cut-off and maintaining the temperature inside the cylinder at a temperature prior to the fuel cut-off; providing an intake throttle valve in an intake pipe and suppressing temperature decrease inside the cylinders by throttling the air intake, which causes cooling inside the cylinders, with this throttle valve when fuel injection is cut off; and providing an exhaust throttle valve in an exhaust pipe and throttling the exhaust gas with the throttle valve during the fuel injection cut off to retain part of the exhaust gas inside the cylinder and suppress the temperature decrease (for example, Japanese Patent Applications Laid-open publication No. 2002-155765).
However, with the above-described countermeasures, the appropriate combustion during subsequent small fuel injection is guaranteed and white smoke generation is prevented by maintaining the temperature inside the cylinders during fuel injection cut-off at a level prior to the fuel injection cut-off with a variety of devices (glow plug, intake throttle valve, exhaust throttle valve). Therefore a device (glow plug, intake throttle valve, exhaust throttle valve) for maintaining the temperature inside the cylinders is required and cost is increased.
Furthermore, when a glow plug system is used even if the glow plug is actuated in an intake air flow, the temperature inside the cylinders actually cannot be maintained at a level prior to the fuel cut-off (temperature at which white smoke can be prevented).